The present invention relates to an improvement in or relating to an apparatus for recording a magneto-optical recording medium in a magnetic field-modulation mode.
The usefulness of optical disks as a large capacity information memory has been noted. One example of such optical disks is magnetic modulation type magneto-optical recording disks, which are expected to be prospectively used as data files. In the magnetic field-modulation type magneto-optical recording a beam of light from the laser of an optical head is thrown to the recording layer of the magneto-optical recording disk in a DC manner to raise its temperature, and at the same time, an information-modulated magnetic field is applied to the recording layer of the disk by a magnetic head, which is put on the side opposite to the optical head. This permits the overwriting of different pieces of information on one and same recording medium, and therefore, the possibility of use as an overwriting compact disk has been thought of.
As for magnetic field-modulation type magnetic heads or magnetic heads used in the magnetic field-modulation mode, there are two kinds of heads, that is, a floating magnetic head which is responsive to rotation of the disk for floating up above the rotating disk like a magnetic head for a hard disk device, and a non-flying magnetic head. The non-flying magnetic heads include two types, stationary type wherein the head is spaced from the disk surface at a fixed distance and sliding type wherein the head is mounted on a slider such that the head is retracted a fixed distance from the surface of the slider in sliding contact with the disk whereby the head is maintained at the fixed distance from the disk surface during operation. The strength of the magnetic field to be applied to the disk surface will increase with decrease of the distance between the disk and the magnetic head. An interference between the disk and the stationary magnetic head is liable to be caused by the swaying of the rotating disk surface if the disk is bent or deformed. With a view to avoid such an interference a deviation detecting sensor is used to keep the stationary magnetic head at a fixed distance from the rotating disk.
Non-flying type magnetic heads are not responsive to the rotation of the disk, and may be advantageously used for disks rotating at a relatively low speed such as compact disks. These magnetic heads have less troubles caused by projecting objects attached to the disk surface, if any. The magnetic heads equipped with no deviation sensing means are simple in structure and are less expensive.
Non-flying stationary type magnetic heads for magnetooptical recording must be used with their head cores placed an increased distance apart from recording mediums, compared with floating type magnetic heads for hard disk devices, and accordingly a strong magnetic field must be used. In this connection it is necessary that a heavy current, say, 1 A p-p flows in the coil wound around the head core, and it is necessary that a heavy modulation circuit is designed so as to carry such a heavy current. In operation, this current must be reversed repeatedly at an increased frequency, say, 1 MH.sub.Z.
FIG. 3 shows a conventional circuit for generating an information-modulated magnetic field. It comprises a coil L.sub.H wound around the core of a magnetic head and having an inner resistance R.sub.H, and switching elements S.sub.11, S.sub.12, S.sub.21 and S.sub.22, which are responsive to signals from associated control means for opening or closing, thereby reversing the current flowing in the head coil L.sub.H.
These switching elements have an inner resistance, say, 1 to 2 ohms, and therefore, a substantial power loss will be caused when a heavy current of about 1 A p-p flows in these switching elements. The inner resistances of the switching elements will increase with increase of the temperature of the head coil, which is caused by the flowing of such heavy current therein, and the power loss will increase accordingly. Additional power loss will be caused by the resistance of the conductors extending to the head core.
It is, in fact, necessary that a power supply is designed to provide extra power enough to compensate for such power loss, and accordingly the operating efficiency will be lowered.